Generally a pictorial image processing apparatus such as a facsimile adopts a heat sensitive recording method utilizing a thermal printer head element for recording a processed document. In the heat sensitive recording method, the record paper is expensive and has poor preservation of record even if black dots are expressed relatively well by using a special heat sensitive paper recorded by the thermal printer head. Recently a facsimile using a normal paper as a record paper is getting popular, and the facsimile using the normal paper adopts an electrophotographic method utilizing a LBP(laser beam printer) or LED(light emitting diode). However, a resolution is deteriorated owing to a quality of the normal paper and a minute detail is not expressed well in the electro-photographic method as compared with the heat sensitive recording method. Consequently a dark recorded paper is produced. Accordingly the facsimile using a normal paper should increase a resolution of its recording device more than a resolution of a manuscript scanner, and a number of data processed and transmitted to the recording device in proportion to the increased resolution. In 1980, Consultant Committee of International Telegraph & Telephone (hereinafter called as "CCITT") recommends that a scanner of G3 facsimile apparatus should have about 203 dots per inch ( 8 mm per character) for a horizontal resolution and about 196 dots per inch (7.7 mm per line of the character) for a vertical resolution. As compared with the recommendation of CCITT, a current recording device of the normal paper facsimile has normally a resolution of 300 dots per inch for a vertical and a horizontal directions. Accordingly the number of data to be recorded should be enlarged vertically and horizontally by 1.534 times. An pictorial image quality of an output is influenced by a method of magnification when the data to be recorded is magnified according to a change of resolution. A zero-order interpolation is used mostly for magnification because of simplicity of embodiment. As the zero-order interpolation repeats simply a pixel of every even number in a horizontal direction and a line of every even number in a vertical direction, the black dots are converted asymmetrically partially, and furthermore it is occurred often that the black dots are piled on one another. Consequently the zero-order interpolation may deteriorate greatly an pictorial image quality of half tone expressing an intensity by a distribution density of random discrete black dots in the same way of an error diffusion method.
There is disclosed a new magnification method utilizing a combination of logical product and sum so as to eliminate such problems as deterioration of pictorial image quality in the zero-order interpolation and to easily perform such a thing, when it is necessary to convert a resolution of the data to be recorded in a normal paper facsimile.
With reference to FIG. 1, a configuration of conventional facsimile system is described as follows. A central processing unit 2 (hereinafter called as "CPU") controls a system according to a given program. A memory 3 stores program data, protocol data and character data, and accesses and/or stores the data by a control of the CPU 2. An operating panel equipment 1 comprises a plurality of keys for generating key data and a device for displaying data of the CPU, and transmits the key data to the CPU 2 if the key data is generated. A charge coupled device 8 (hereinafter called as "CCD") reads pictorial image data from a manuscript and performs a photoelectric conversion of the pictorial image data. A scanner 6 transmits the converted pictorial image data from the CCD 8 to the CPU 2. A modem 4 modulates output data of the CPU 2 into an analog and demodulates received analog data by a control of the CPU. A signal processor 9 decodes and/or encodes output pictorial image data from the scanner 6 and the modem 4. A PSTN line interface circuit 5 establishes a speech loop of a telephone line and interfaces the signal of the modem 4 with a signal of the telephone line by a control of the CPU 2. A printer 7 prints input data by a control signal of the CPU 2.
FIG. 2 illustrates an example of conventional conversion from a resolution of 200 dpi to a resolution of 300 dpi and FIGS. 3A, 3B illustrates an example of a conventional resolution conversion of pictorial image data.
With reference to FIGS. 1 to 3, a conventional resolution conversion method by a magnification utilizing the disclosed zero-order interpolation is described as follows. Pictorial image data of 200 dpi read by the CCD 8 or received from the modem 4 through the PSTN line interface circuit 5 is stored in the memory 3. With reference to FIG. 2, the CPU 2 converts a resolution of first line by writing a pixel of odd number once and writing a pixel of even number twice repeatedly in a horizontal direction (as shown in FIG. 2) after reading by two pixels of the pictorial image data of a first line at a time from the memory 3. After completing a resolution conversion of a first line, the CPU 2 performs a resolution conversion of a second line in the same way of processing the first line, and writes the second line of resolution conversion one more time repeatedly under the second line in a vertical direction. After finishing the resolution conversion, the converted pictorial image data is stored in the memory 3 and transmitted to the printer 7 for printing. By repeating such an operation, the CPU 2 converts an input pictorial image signal of resolution of 200 dpi as shown in FIG. 3A to pictorial image data of resolution of 300 dpi as shown in FIG. 3B by writing a pixel of even number twice repeatedly in a horizontal direction and a line of even number twice repeatedly in a vertical direction.
Since pictorial image data of resolution of 200 dpi is converted to pictorial image data of resolution of 300 dpi by writing twice repeatedly a pixel of even number in horizontal direction and a line of even number in vertical direction respectively, a horizontal and a vertical stripes are appeared, pictorial image quality is deteriorated, and pictorial input image signal is distorted.